nl80211: Add flag attribute for RRM connections

Add a flag attribute to use in associations, for tagging the target
connection as supporting RRM. It is the responsibility of upper
layers to set this flag only if both the underlying device, and the
target network indeed support RRM.
To be used in ASSOCIATE and CONNECT commands.

Signed-off-by: Assaf Krauss <assaf.krauss@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>